<h2>DESCRIPTION</h2>

<em>v.proj</em> allows a user to convert a vector map in a specified mapset
of a specified location (different from current) with projection of input
location to the vector map in a current mapset of current location with
projection of current location (both projections are defined by
corresponding PROJ_INFO files). The projection information is taken from the
current PROJ_INFO files, as set and viewed with
<em><a href="g.proj.html">g.proj</a></em>.

<p>
For an introduction to map projections (with PROJ),see the manual page of
<a href="r.proj.html">r.proj</a>.

<h2>NOTES</h2>

If <b>output</b> is not specified it is set to be the same as input map
name.

<br>
If <b>mapset</b> is not specified, its name is assumed to be the same
as the current mapset's name.

<br>
If <b>dbase</b> is not specified it is assumed to be the current
database. The user only has to specify <b>dbase</b> if the source
location is stored in another separate GRASS database.

<br>
If <b>smax</b> is set to <b>0</b> the automated vertex densification is
disabled (not recommended).

<p>
<em>v.proj</em> supports general datum transformations, making use of the
<em>PROJ</em> co-ordinate system translation library.

<p>When projecting into a latlon location, east coordinates are wrapped 
by the proj4 library to fit into the range -180,180. This is in most cases 
appropriate, but can cause errors the input vector crosses the datum line 
at 180E/W. In this case wrapping of east coordinates to -180,180 needs 
to be disabled with the <b>-w</b> flag.

<p>When reprojecting massive point clouds for which topology is not necessary,
the user can set the <b>-b</b> flag to suppress the building of topology of
the output map.

<p>
In order to preserve spatial detail, <em>v.proj</em> performs automated
vertex densification (as an alternative, <em><a href="v.split.html">v.split</a></em>
could be used before reprojecting. Without vertex densification, depending on
the source and target CRS (Coordinate Reference System), geometries can be
substantially deformed (straight lines become curves, squares become
trapezoids, etc). The densification of linear features can help to avoid 
topological errors.

<h2>EXAMPLE</h2>

Reprojection of a vector map from another location and mapset into the current mapset:

<div class="code"><pre>
v.proj in=mymap location=latlong mapset=user1
</pre></div>

<h2>REFERENCES</h2>

<ol>
  <li> Evenden, G.I.  (1990) <a href="https://proj.org">Cartographic
      projection procedures for the UNIX environment - a user's manual.</a>
    USGS Open-File Report 90-284 (OF90-284.pdf)
    See also there: Interim Report and 2nd Interim Report on Release 4, Evenden 1994).
  <li> Richards, John A. (1993), Remote Sensing Digital Image Analysis,
    Springer-Verlag, Berlin, 2nd edition.
</ol>

<a href="https://proj.org">PROJ</a>: Projection/datum support library.

<p>
<b>Further reading</b>
<ul>
  <li> <a href="https://www.asprs.org/asprs-publications/grids-and-datums">ASPRS Grids and Datum</a>
  <li> <a href="http://geotiff.maptools.org/proj_list/">Projections Transform List</a> (PROJ)
  <li> <a href="https://proj.org/operations/index.html">Coordinate operations</a> by PROJ (projections, conversions, transformations, pipeline operator)
  <li> <a href="http://www.mapref.org">MapRef -
      The Collection of Map Projections and Reference Systems for Europe</a> 
  <li> <a href="http://www.crs-geo.eu">Information and Service System for European Coordinate Reference Systems - CRS</a>
</ul>

<h2>SEE ALSO</h2>

<em>
<a href="g.proj.html">g.proj</a>,
<a href="m.proj.html">m.proj</a>,
<a href="r.proj.html">r.proj</a>,
<a href="i.rectify.html">i.rectify</a>,
<a href="r.stats.html">r.stats</a>,
<a href="v.sample.html">v.sample</a>,
<a href="v.split.html">v.split</a>,
<a href="v.surf.idw.html">v.surf.idw</a>,
<a href="v.surf.rst.html">v.surf.rst</a>
</em>

<h2>AUTHORS</h2>

Irina Kosinovsky, US ARMY CERL
<br>
M.L. Holko, USDA, SCS, NHQ-CGIS
<br>
R.L. Glenn, USDA, SCS, NHQ-CGIS

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